The sun warms our planet, and the earth releases a huge spectrum of radiation in the universe. Light is only a small part of this spectrum, namely, the visible portion of the spectrum-colors of the rainbow.

Dark matter is a hypothetical type of matter. It does not emit with electromagnetic radiation. Light emit with electromagnetic radiation, so we can see light in electromagnetic spectrum. But we cannot see dark matter. It is invisible in electromagnetic spectrum.

In the universe, there are three types of galaxy. First one is Dwarf Galaxy. It is a category of smallest galaxy. In this category, many galaxies across only 200 light years. and in this type of galaxies have few millions of stars.